Aleph One: Marathon

English:

Aleph One is an Open Source 3D first-person shooter game, based on the game Marathon 2 by Bungie Software. It is set in a Sci-Fi universe dominated by deviant computer AIs and features a well thought-out plot. A conversion of Marathon 1 called M1A1 and many third party scenarios and net maps are also available.

Controls:
Luckily they are redefinable. Personally I didn't like the default settings (num keys 4,8,6 = move, space = fire). So I switched the mouse on and set the right mouse button as move forwards and the left mouse button as fire.